AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10
Contents
1. AN 002 APPLICATION NOTE AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 by Daniele Ponteggia dp audiomatica com INTRODUCTION The acoustical response of a loudspeaker is angle dependent A single on axis re sponse measurement cannot accurately characterize the system It is possible to generalize and treat the system as single electrical input to multiple acoustical output S Figure 1 Loudspeaker radiation model It is common practice to collect loudspeaker responses on axis and off axis by means of different relative loudspeaker to microphone positions The response is usually sampled at a given fixed resolution along the horizontal and vertical planes of the loudspeaker These sets of measurements are often used to create technical docu mentation in form of polar pattern graphs A good description on how to measure the polar response along a single plane is available on Testing Loudspeakers by Joe D Appolito 1 and on CLIO manual 2 The horizontal and vertical polar patterns are only a subset of the complete radiation of the loudspeaker into the surrounding space If the complete spatial response of the loudspeaker needs to be characterized a more complete description of the spatial sound radiation is needed COORDINATE SYSTEM DEFINITION We model the source as a point and sample the response over a sphere surrounding the source The point source model assumption can be objectionable but if the mea surement distance2. Figure 8 Frequency responses The 3D naming scheme is also compatible with the CLIO directivity module The first part of the file name the string filename lt phi 100 gt can be seen as the prefix of a set of measurements which are an half polar 90 0 S PRU T 80 0 p INL LL In fact the azimuth angle 9 is fixed the polar angle 9 ranges from 0 to 180 de grees this can be seen as a slice of the balloon taken at the azimuth angle 11 With the Outline ET250 3D turntables the zero position of the turntable is lost at every power down please return the turntables at the physical zero position before powering off the units 15 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 In the following example we will display the directivity of the 10 azimuth angle half polar Figure 9 10 azimuth angle half polar The root file name to choose is filename 1000 then set Z Start 0 Z Stop 180 and Z ref 0 as in the following settings screenshot Waterfall Directivity amp 3D Settings General Set OF Data Files 20 Root File Name Start Frequency Hz Stop Frequency Hz 122339 Save Settings Default Cancel Then the directivity can be seen in form of classic polar plots figure 10 or as water fall plot figure 11 or colormap directivity plot Notice the fact that with these tools only a small amount
3. i e the sphere radius is sufficiently large compared to the source dimension the model can be accurate 3 To represent the three dimensional geometry of the problem we use the spherical co ordinate system A point into this system is described by means of three coordinates AN 002 1009 1 33 AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 the radial distance of a point from the origin the zenith angle from the positive z ax is to the point and the azimuth angle from the positive x axis to the orthogonal projection of the point in the x y plane 4 If we position the loudspeaker into the origin with the z axis emerging from the front baffle as depicted in the following figure Figure 2 CLIO coordinate system we can immediately visualize the representation in spherical coordinates The radial distance is fixed and is the balloon radius 9 is the zenith angle also called here polar angle and e is the azimuth angle We can compare this model to the earth globe we can think at the loudspeaker placed at the center of the earth with the front baffle facing towards the north pole every meridian at a given longitude is a loud speaker polar and the latitude is the polar angle For every triplet Ir 6 0 thus for every point into the space S surrounding the loud speaker we will have a transfer function H r 0 BALLON DATA REQUIREMENTS The main usage of balloon measurements is the source modeling i
4. 9 1 14 0 68 1 54 12 10 122 7 2 42 D 55 ld 2 99 LeTo 334 7 2 69 3 00 4 76 215 Jue 4 05 5 dTa 2 49 4 14 Sa 9 Peg d sd 8 59 3213 This tab text file must then be authored with the CLF editor viewer which is available on request from the CLF group CLF reader viewer trial rogers tab Ele Edit Options Help Model 3D balloon Cabinet 30 representation Harne Weight 1 00 kg Descr description _ r r T Colors r L U C Radiaion fullsphere Mounting Type passive Manufacturer M ame ILS 3 5 Web site Measurement Contact name E mail emailaddress 0000 Date Distance 1 00 m Env ws Inp voltage Es ami mm Es ES uma Wami mm Wma B 100 125 160 200 250 315 400 5 630 gt Electro acoustical data Sensitivity 888 921 338 940 925 904 885 918 914 dB gt Impedance 150 15 0 15 0 150 150 150 150 180 150 w hor Sar 327 287 350 231 er Ae w ver 273 223 221 215 235 134 Aia 25 29 28 25 25 13 58 47 dB Ax Spect 89 8 921 938 940 925 904 88 5 91 8 91 4 input power yw Equiv size w Avg impedance 15 00 Ohm Cabinet 3D representation Rectangular Re max Sensitivity Back CLF2 version final Polars Electro acousticaldata Balloon spectra CLF A
5. Directivity balloons 28 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 Balloon Export File amp Export Format Output format Impulse Responses Dutput folder C Documents and Settings D aniele Desktop Rogers_3D General Information On Axis Response Impedance amp Power Truncation TS nel 7 73 Enable Truncation Truncate text file Ok Cancel Figure 24 Impulse responses balloon export features We do not want here to enter into the EASE SpeakerLab details it is interesting here to show the import data window Importing CLIO data is very easy as the EASE SpeakerLab import feature is very easy to understand 48 Import Impulse Response Meridians Horizontal Resolution Parallels Vertical Resolution found found found found Tound Resolution x Resolution 5 v tt found Front Half Only found None Full Sphere Order of Measurements 5 found Horizontal 50054 found Start From 0 Position found O Vertical 5500 found Q Left Top bad found Quarter 907 found Axial Right Bottom found Options Number of Files to Import Use Redundant On Axis Measurements for Re Normalization Recommended Number of Files missing Figure 25 EASE SpeakerLab Import Impulse Response Window In our case the optio
6. K 4 iU Documents 50 0 50 0 1D 30 Polar Azimuth 10 0 Start 10 0 5 0 Step 5 0 180 0 Stop 355 0 0 0 0 0 Tumtabe 10N Tumtabe20N Autosave Syne Options gt Stark Stop ll Continue 10 In the 3D mode only computer controlled turntables as the Oultine ET250 3D and the LinearX LT360 can be used if two turntables are not available the user can choose as second turntables the manual turntable This means that the user needs to manually provide for the correct azimuth rotatioin of the loudspeaker 13 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 If we setup the angles as in the above figure Polar 0 Azimuth 2 start 0 0 step 5 5 stop 180 360 by clicking on the Start button on the Turntables Settings we will measure the full sphere balloon with 5 degree resolution In this case the naming scheme is composed of a filename plus two suffixes filename phi 100 theta 100 mls the first angle is the azimuth and the second angle is the polar The following picture can help to understand the relationship between the polar 9 and azimuth angles and a given file of the saved set with the above naming scheme 270 90 Figure 7 Azimuth and polar angles To summarize there are five steps to follow to perform a balloon measurement set with CLIO 10 1 Preparation of the m
7. high resolution complex response data sampled at 5 degree or finer spatial resolution 6 with these ele ments the simulation of array systems can be carried out with high accuracy Since the complex data is required instead of the SPL modulus data only the interpo lation of the complete balloon data from the horizontal and vertical planes data if mathematically feasible is certainly highly questionable While in the past it has been acceptable to interpolate magnitude only data to create matrices of sound pressure levels the interpolation of complex data to create high resolution complex data bal loons is not acceptable If the source has to be modeled using the complex data the measurement of the complete balloon response sampled at the desired angular resolution is needed This involve a much more complicated measurement hardware than the simple plane polar measurements LOUDSPEAKER POSITIONER We want to sample the response into the a sphere surrounding the loudspeaker We will collect a set of responses by varying both the 9 zenith angle and the 4 azimuth angle There are some different ways to do that using a set of n microphones and collect n responses at the same time using a set of n microphones and collect a single response at time using a single microphone and moving it around the source using a single microphone in a fixed position and rotating the loudspeaker It is also possible to combine two of the ab
8. r 3402 4 2 with d being the measuring distance and x the distance between an acoustic source and the Point of Rotation Thus when modeling a large source as a point source and measuring the response over a sphere surrounding it large distances are necessary As a solution to this problem it was recently introduced in EASE a new loudspeaker model GLL where it is possible to combine into a loudspeaker model different point 3 Outdoor measurements are highly discouraged since the polar measurements can last for few hours and the change of environmental conditions can severely affect the reliability please note that this can be also a problem indoors Furthermore outdoor wind and noise can affect the measurements 7 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 sources in different points in space It is thus possible to measure every single source as a point source at a shorter distance A limitation of the measurement distance is usually due to the available room dimen sions and type There are three basic possible room types fully anechoic semi anechoic and non anechoic In a fully anechoic space apart from the measuring distance the only problem to face is the mechanical stability of the test gig the turntable must lie on an hard surface to avoid oscillations Some positioning tools that are able to handle heavy loudspeaker rely on arms with wheels these tools are very difficult to use ove
9. setup dimensions is it possible to calculate the threshold frequency Is it also possible given the height of the loudspeaker position the measurement distance d and the threshold frequency to calculate the minimum room dimensions 2 d E LOW 219 H E h 2 d ay _ LOW 99 W 2 4 d 2 f iow D d 2 d As said before where a large anechoic room is not available a practical solution to perform 3D polar measurements at large distances and wide bandwidth is a large low reverberation room with hard floor and with an absorptive treatment on the floor be tween the source and the microphone MEASUREMENT ANGULAR RESOLUTION Since it is possible to gather only a finite number of responses it will be necessary to define a rule to sample the surface S around the source Under the assumption of a point source it is possible to sample a given number of points over a sphere surface with radius r The sphere radius r is the measurement distance In order to characterize the complete emission of a source it is necessary to sample over the complete sphere in case of symmetry of the emission it is possible to sample only a semi sphere or a quarter sphere The resolution of both the polar angle 0 and the azimuth angle must be specified It seems reasonable to use a regular sam pling interval as an example of 5 degrees for both angles 9 and 6 Non regular sampling of the sphere of emission of a loud
10. BOX WITH HORIZONTAL SYMMETRY In this example we measure the balloon of a 2 way small loudspeaker box with hori zontal symmetry and then we export the data to create a CLF model and an EASE GSS high resolution sound source model Figure 16 Small 2 Way Loudspeaker By looking at this loudspeaker it is possible to identify an horizontal symmetry since the drivers are horizontally positioned at the center of the front baffle and the cabinet is a simple rectangular box 0 95 0 15 0 8 0 95 0 15 0 8 Point of rotation 0 0 0 0 95 0 15 0 8 gt 00 0 95 0 15 0 8 2 0 95 0 15 0 8 Figure 17 Cabinet Coordinates Relative to the Point Rotation 23 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 The first step is to define the point of rotation of the system and identify the loud speaker dimensions relative to that point In this case we choose as a point of rotation the geometrical center of the cabinet cabinet coordinates are showed in figure 17 We arranged a setup comprising two Outline ET250 3D turntables connected to form a positioning machine this is basically the same system showed before in this docu ment The measurements are carried out in our laboratory due to space constraints this measurements cannot obey the minimum source to microphone distance require ments and their validity is limited The distance between point of rotation an
11. CLIO 10 The automated procedure can also be halted and resumed in a later time With CLIO 10 there are two different polar modes 1D polar mode and 3D polar mode The 1D polar mode can be seen as a legacy mode and is the same as the pre vious software versions the 3D polar mode is the new one it has been introduced to manage the measurement of loudspeaker balloons The 3D mode is available only under the QC version of the software 1D Polar Mode The 1D Polar Mode perform a set of measurements automatically by varying one pa rameter and controlling a single turntable It is intended as legacy mode that is compatible with older versions of the CLIO software If you are coming from a previ ous CLIO version please notice that the turntable is controlled from the Turntables Settings dialog instead of the External Hardware dialog Here we do not want to go into the details that can be found on the CLIO 10 user manual 3D Polar Mode The 3D Polar Mode can perform set of polar measurements using one or two computer controlled turntables In its common usage we need two computer controlled turntables connected to the PC and we need to setup the Polar and Azimuth angles in the Autosave Settings dia log In this dialog we need also to set the filename the autosave folder and the file format binary and or text Turntables Controls Turntable 1 Turntable 2 AutoSave Settings E3 TAVOLA T TAVOLA2 EE Bn 256 pt o 4
12. WEIGHT 1 lt MINBAND gt 100 lt MAXBAND gt 20000 lt gt name lt gt emailaddress lt MEASUREMENT DATE gt 2009 Nov 10 lt MEASUREMENT NOTE gt lt MEASUREMENT ENVIRONMENT gt lt MEASUREMENT DISTANCE gt 1 MEASUREMENT INPUTVOLTAGE lt gt passive SOBNSITIVITYS 99 02 D dd 92 70 94 01 94204 90 42 98 22 dls TS 91 41 912024 922520 91 67 92 30 90 60 88 45 90 99 90 38 90 74 TD dE 92 74 94 44 ILGS lt SPNSTITIVITY TNFO2 gt lt IMPEDANCE gt TOU 15 00 15 00 VOS 159 09 19400 15 00 15 00 153 00 03200 1500 1500 15300 15 00 15 00 Tos QU 154 00 Lasd 19 00 15 00 19 00 154308 lt IMPEDANCE INFO gt lt TOTMAXINPUT gt lt power gt 100 00 lt METHOD gt lt 268 1 gt lt RADIATION gt lt fullsphere gt 31 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 lt AXIAL SPECTRUM gt lt nodata gt lt nodata gt nodata lt nodata gt lt nodata gt lt nodata gt 89 85 92 12 93 78 94 01 OZ 52 90 42 098 53 21472 91 41 22 258 91 02 356 306 91 67 92 30 90 60 68 45 88 59 90 38 90 74 89 70 91197 92 74 94 44 91 65 XAXIAL SPECTRUM INFO measurement info lt BALLOON SYMMETRY gt none lt BALLOON ARC ORDER gt lt reversed gt lt ROTATE gt 90 lt BALLOON REF gt lt relative gt lt SIGN gt lt reversed gt lt BAND gt 100 0 O 211 0 67 ae 0 03 0 80 0 01 L5 9274 0 93 0
13. d of the import process the balloon show up it is possible to rotate the bal loon and to inflate deflate it which means using different ranges for the balloon radius It is possible to color the balloon where different radius are mapped using the classic CLIO colormap shading It is also possible to superimpose a reference balloon The 3D analysis tool allows also to export the measured data to the most used loud speaker directivity formats EXPORT TO EASE EASE is a widely used software for electroacoustic simulations Basically there are two types of source models SPK models and GLL models The directivity of SPK models is based on a tabular data approach where for each fre quency band in third octave from 100 Hz to 10 kHz there is a table of the SPL 20 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 attenuation as function of the 0 and 4 angles with a 5 degree resolution The GLL Generic Loudspeaker Library models are based on an object oriented ap proach one of the object of a GLL is the GSS source model which describes the directivity and other characteristics of the source The GSS can be still based on the tabular data approach but that can also store the directivity as a set of high resolu tion impulse responses with an angle resolution finer up to 1 degree CLIO 10 can export data to create SPK or GSS source models EASE SPK models The SPK model is stored in a set of proprietary binary fil
14. d the microphone is 50 cm and the first re flection is coming from the floor the point of rotation and microphone height is 140 cm With this arrangement we have a reflection free environment of only 6 6 ms which means a cutoff frequency of 150 Hz We start measuring the on axis response of the source using the MLS amp LogChirp mod ule in this case we choose a 16k MLS signal as stimulus MLS Impulse Response 4 29 2008 6 11 22 PM m T N luas s 0 1 5 3 0 4 5 6 0 7 5 9 0 11 12 ms 14 15 Ax 1 4746 ms 0 0008 Az 0 5073m 8 1356 ms By 0 0008 Pa Bz 2 7986 m dBSPL Unsmoothed 48kHz 16K Rectangular Start 0 00ms Stop 8 13ms FreqLO 123 08Hz Length 8 13ms Figure 18 On axis impulse response As illustrated in figure 18 the time window stop time must be set to 8 14 ms this set ting will be the preset for all the polar measurements Getting the correct on axis position between the source and the microphone can be very difficult especially if the microphone distance is of several meters A trick that can be used is to repeatedly measure the response and moving the turntables with 24 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 small increment until the response is not reaching a maximum which supposedly is the on axis value Another opportunity if the source has symmetries is to move the source 10 degree of axis along one angle collect a measurement move the sourc
15. dspeaker polar radiation measurements 33 33 www audiomatica com
16. e space is non anechoic means also the use of a really high ceiling at least 7 24 m A solution to the problem can be achieved eliminating the floor reflection using highly absorptive material placed on the ground between the source and the mi crophone position This leads to a practical height for the loudspeaker allowing measurement down to the 100 Hz range in large closed spaces If a non anechoic space is used to perform polar measurements it must be noted that the room rever beration time must be short enough to avoid time aliasing between successive measurements if using an automated process the operation must be triggered to let the acoustic energy in the room to decay A detailed and elegant explanation of the reflection free environment can be found on 5 where an ellipsoid of free reflections is defined Here are reported only few practi cal considerations if the room has a shoe box shape with the loudspeaker and the microphone placed as in figure 4 It is also possible to predict the effect of the position of the point sources and the spatial effect of the crossover network 5 This is possible with CLIO 10 using the turntables control dialog 8 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 ceiling reflection direct path source wall H receiver wall mE 440 Figure 5 Rectangular room reflections given the room and measurement
17. e to the 10 degree angle collect a new measurement and check if the two responses match In case they do not match move the microphone or set a different turntable reference 0 angle Given the fact that our source has an horizontal symmetry the number of measure ments that must be carried out can be reduced respect the full sphere Since we are interested in creating an EASE model we decide to use 5 degree angular sampling The source can be sampled over half sphere it is possible to choose which half to measure Here we will sample the right hemisphere with angle ranging from 270 degrees up to 355 and from 0 and up to 90 degrees Figure 19 Loudspeaker horizontal symmetry The automatic procedure do not allow to do this this is not possible to use a start an gle greater than the stop angle so we will use here a small trick to perform the automatic measurement procedure without any manual intervention We will set the autosave as illustrated in figure 20 Then we will reset the azimuth turntable O position with the loudspeaker in horizontal position such as illustrated in figure 21 notice that the axis are rotated by 90 degrees in respect to the previously defined CLIO reference system At this point we are ready to start the automatic procedure by pressing the start but ton on the Turntables Control dialog remember that the two turntables must be connected Once the procedure is completed it is possible to open the 3D a
18. e turntable require its software to setup a suitable IP that can be accessed by the computer where the CLIO 10 software is running 2 A device driver dll must be present into the CLIO 10 program folder basert dll for the Outline ET250 3D This dll is not shipped with CLIO and must be sup plied by the turntable manufacturer 5 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 Here is an example of a LAN connection of the PC with CLIO 10 software and two Out line ET250 3D turntables ET250 3D POLAR 192 168 0 69 NET SWITCH ET250 3D AZIMUTH PC 192 168 0 70 CLIO 8 192 168 0 1 We used the Outline XP Commander software to set up the two turntables with the above IP addresses Then we connect the CLIO 10 software using the Turntables Control dialog Turntables Controls Turntable 1 Turntable 2 Polar Azimuth 00 Autosave Sync Options db The Option dialog can be opened by clicking on the button Turntables Settings Turntable1 Turntable2 192158059 1921680270 Port 6666 Port 6667 0 Delay 0 OK Cancel Once the turntables are connected to the LAN and powered up it is possible to control them with the CLIO 10 by pressing the buttons Link tumtabie1 and Link Tumtabte2 6 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 If the connection is established properly the name and the cur
19. easurement setup Depending the final application of the measurement set and the available envi ronment the user choose the measurement distance d and the angular resolution If the room is not anechoic the user must arrange a convenient measurement setup and analyze the energy decay to decide the delay time be tween measurements 2 Setup of the CLIO autosave Depending on the source symmetry and the angular resolution the user need to fill the Autosave settings dialog 14 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 3 Reset to the start position The loudspeaker positioner must be put in the starting position this can be eas ily accomplished by pressing the Sync button on the Turntables Control panel Some care must taken in setting up correctly the zero reference of the two turntables according to the reference system previously described This will be more clear in the following examples 4 Run the measurement set 5 Wait for the completion MEASUREMENT ANALYSIS The measurement process creates a big amount of data in form of impulse responses mls files These files can be obviously singularly analyzed using the MLS amp LogChirp control panel MLS Frequency Response mens ail ki IL ELTE A TA NATIN I a CL MW ALL E 1 LLL IM 50 100 200 500 Hz 10k 20k CHA dBSPL Unsmoothed 48kHz 16K Rectangular Start 0 00ms Stop 7 79ms FreqLO 128 34Hz Length 7 79ms
20. es that are editable using the EASE SpeakerBase module The link between the measured balloon and the SPK mod el is a text file xhn which contain data on the directivity of the balloon and some accessory information The CLIO 10 3D directivity module is able to export the balloon in this format to cre ate an SPK model the xhn file must be imported using EASE SpeakerBase It must be noted that CLIO 10 is able to export xhn files containing only magnitude data phase data is not included Together with the directivity CLIO 10 can export an on axis response and the imped ance in third octaves This speed up the editing process while into the SpeakerBase EASE GLL models The GLL model is stored again in a proprietary binary file the GLL model can be edit ed using the EASE SpeakerLab software The source definition menu of the SpeakerLab can import set of measured impulse responses with a given resolution and symmetry EASE SpeakerLab can import CLIO time data impulse response text files with the CLIO naming scheme except for the fact that the filename must be IR The CLIO 10 3D directivity module can automatically mass export the set of measured binary mls impulse response files in the time data format requested by the EASE SpeakerLab EXPORT TO CLF The CLF Common Loudspeaker Format is a freely available format created and sup ported by a group of software developers and CLF data authors The format is based on a binary
21. f Outline ET ST turntables for balloon measurements With two Outline ET250 3D turntables it is very easy to build a positioner The CLIO 10 software can get full control of the Outline ET250 3D turntables We built a loudspeaker positioner using two Outline ET250 3D turntables and standard 45 x 45 mm aluminum profiles With the same profiles we realized a simple clamp to hold the loudspeaker Even though our loudspeaker positioner is just a proof of concept realization and is not intended to be of real world usage it is very simple as it was built from stock items in less than 10 minutes Note that suspending heavy loads as some loudspeaker boxes can be harmful Please be extremely careful when suspending loads 2 Itis possible to control also the LinearX LT360 turntable but we found the Outline ET250 3D construction sturdier and our test jig was easier to assemble 4 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 E b a Y p Figure 4 Loudspeaker positioner The turntables can be connected to the CLIO 10 software using the turntables dialog window to access to the dialog click the button here is it possible to choose the model of each turntable and enter the connection parameters Before connecting the turntables to the software two steps are required 1 The turntables must be correctly setup using the software provided by the man ufacturer as example the Outlin
22. file which is compiled starting from a text file using the CLF editor soft waret The approach is similar to the previously described SPK In this case the data is again in tabular format with 5 degree resolution and third octaves from 25 Hz to 20 kHz Detailed information can be found on the www clfgroup org web site The CLIO 10 3D directivity module is able to export the balloon in the CLF v2 tab text file format As in the case of xhn files CLIO 10 can export an on axis response and the imped ance in third octaves This speed up the editing process while into the CLF editor 13 The CLF Editor is freely available on request from www clfgroup org 21 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 Balloon Export File amp Export Format Output Format EASE xhn Output file General Information Loudspeaker Model Name Manufacturer Manufacturer Mame r r r LU U U Frequency Range Hz 10000 On Asis Response MLS file Tim Use Balloon Data Level Shift dE lt Meas Distance m 1 Drive Level pa 1 Impedance Power Impedance File Use Nominal Impedance ohm Power 100 Truncation Cancel Figure 15 CLIO 10 3D export form 22 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 EXAMPLE MEASUREMENT OF THE HORIZONTAL HALF SPHERE BALLOON OF A SMALL LOUDSPEAKER
23. n simulation soft ware At the beginning of computer simulation of sound sources there were limits on PC processing power and memory The acoustic sources were modeled using a set of attenuation matrices each containing the sound level pressure in respect to the on axis level for a given octave or third octave band The spatial resolution ranged from 15 to 5 degrees The degree of accuracy of these simulations were not satisfactory for some applications one of the most lacking features was the possibility to correctly model arrayed systems In those days the requirements for the accuracy of the bal loon directivity data were not strict a common practice was to measure only the 1 In this case since we are describing the coordinate system for the measurement of the polar response the radius is the measuring distance It is necessary to not confuse this with the loudspeaker model that will be created using these measurements The model is often referred to 1 m on axis measurement but this is just a convention and measurements needs to be carried out in the far field 2 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 horizontal and vertical polar and mathematically interpolate the remaining data In the recent years the mutual improvement of PC hardware and simulation software has removed the previous constraints this has raised the requirements on balloon data to an higher level The sources are now modeled using
24. n to select are 5 degrees resolution Horizontal symmetry and Start From Bottom The software check for the presence of the needed files in the se 29 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 lected folder Pressing the import button will start the import process at the end of the process the data is in GSS format ready to be edited into a GLL model View GSS Speaker Temporary File Edit View Graphs Bandwidth Frequency 4000 Hz Data Shown Speaker Manufacturer Resolution High Res 10 10 Symmetry Horizontal Display Parameters Frequency 4000Hz 1 3rd Octave del Mee prm Figure 26 Balloon Imported in EASE SpeakerLab In fact our procedure here generate only directivity information some items must be added to the GSS model as power handling and impedance but these topics are out side of the scope of the present document Please consult software manufacturer specific documentation When editing the loudspeaker model into EASE SpeakerLab some care must be made in drawing the case of the source in fact here we are dealing with an ideal point source that we measured rotating around the defined Point of Rotation POR The data annotated in figure 17 may help to create a proper case drawing for the point source as it gives the case and POR coordinates EXPORT TO CLF FORMAT The CLF format uses a tabular approach to store the directi
25. nalysis menu and load the measured data 25 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 AutoSave Settings j Bin Tet 2562 Path Daniele Desktop Rogers 3D File Name Rogers 1 30 Polar Azimuth 1 0 Start 10 0 5 0 Step 180 0 Stop 180 Cancel Figure 20 Autosave settings Azimuth turntable Figure 21 Horizontal symmetry autosave start position The correct setting for the analysis of the collected data are reported in figure 22 we must use an Half symmetry and a Rotation of 90 degrees to convert the 0 measured azimuth angle to 270 degrees 26 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 Waterfall Directivity amp 3D Settings General Set Of Data Files Foot File Mame Start Frequency Hz 20 rc Stop Frequency Hz 122333 Symmetry Half Rotation 90 Save Settings Default Cancel Figure 22 3D analysis settings The CLIO software then will check for data consistency of the file set then pressing the start button in the Waterfall Directivity amp 3D menu will start the import process This will take few minutes At the end of the import process it is possible to inspect the measured data in form of directivity balloons at third octave standard frequencies figure 23 EXPORT TO EASE HIGH RESOLUTION MODEL We export the measured data to create a GSS EASE directivi
26. of the data collected during the 3D measuring process is ana lyzed in particular the classic polar plot show only one frequency of a single polar 16 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 RefO 1 3 Octave Figure 11 Waterfall directivity of an half polar 17 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 CLIO 10 feature a 3D analysis module This module allows to visualize the response balloon at the standard third octave frequencies and to export the data in different forms EASE xhn ASCII format CLF ASCII format Time Response txt files for import with EASE SpeakerLab The 3D analysis module can manage the entire set of measured impulse responses with the naming scheme and symmetry as previously described The analysis module is the natural counterpart of the 3D measure automation The 3D mode of the Waterfall Directivity amp 3D module can be accessed by selecting the 3D from the drop down menu 1 3 Octave T di e th e e d d 4 1000 P 0 dB 0 0 1 3 Octave Reference Balloon Range 24 dB Figure 12 3D analisys window The settings of this menu are quite simple being the Root File Name Symmetry and Rotation The Root File Name can be choose pressing the browse button and then se lecting any file of the data set 12 Please note that while the 3D autosave allows for different angular resolutions the 3D analysis module accept onl
27. ove as an example rotating the loudspeak er with a set of microphones placed on an arc over the loudspeaker Every approach has its own pros and cons In our experience a reliable and viable way is to use a single microphone in a fixed position and a computer controlled loudspeak er positioner to aim the source along the desired direction This approach is the natural extension of the single plane polar measurements carried out using a computer controlled turntable In respect to the single turntable ap proach here we need a much more complicated hardware in order to rotate the loudspeaker over the two polar and azimuth angles as indicated in figure 3 The two rotation axis can be obtained using a custom robot positioner or using a cou ple of computer controlled turntables mechanically connected 3 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 azimuth A Figure 3 Rotation axes Here is reported an example of the usage of two Outline ET250 3D turntables to build a loudspeaker positioner The Outline ET250 3D turntable is a new generation devices that can communicate in a bidirectional way with a PC using the Ethernet port The previous generation of turntables as the Outline ET ST series did not provide a real communication with the PC waiting for a TTL pulse to start to rotate for a given fixed angular value This together with mechanical torque limitation do not allow the us age o
28. r an anechoic cham ber cable floor Regarding to the measurement distance to get 8 m distance between source and microphone taking into account the fact that the dimension of the loud speaker positioner is not negligible needs a very large and expensive chamber In semi anechoic or non anechoic spaces it is easier to achieve large measurement distances but here we need to face problems coming from the room reflections These must be windowed out from the measured responses With CLIO it is possible to window the impulse responses but the resolution of the measurement is affected by the available free reflection time window Nearer the reflections shorter the win dow lower the measurement resolution The window length sets a frequency threshold above the measurement is reliable In brief early reflections means a short time window hence an high frequency threshold The formula for the frequency threshold is quite simple 1 To get a sufficiently high frequency threshold the loudspeaker must be placed enough away from boundary surfaces In practical terms for a threshold of 100 Hz the need ed reflection free time window length is 10 ms Taking into account the travel time of the sound from the source to the receiver at a measuring distance of 6 m with a speed of sound of 340 m s the minimum distance from the first reflecting surface is 3 62 m This means that is needed to put the loudspeaker over a quite high pole or suspend it If th
29. rent rotation angle of each turntable is displayed on the turntables dialog Turntables Controls Turntable 1 Turntable 2 TAVOLAI TAVOLA2 Ho 4 o _ _ Turntable 1 N Turntable 2 N Autosave Sync Options gt Start Stop Continue By means of the buttons of the dialog it is possible to move the turntables in real time To get a detailed description of the control panel usage please consult the CLIO 10 user manual To get more information on the turntables please check the manufacturers web sites www outline it and www linearx com Once a loudspeaker positioner is available the problem of pointing towards a given di rection is solved There are still some problems that needs to be addressed before trying to measure the balloon response MEASUREMENT DISTANCE A first question to answer is the definition of the the measurement distance which is in turns the measurement sphere radius The distance must be large enough to limit the apex error and diffraction effects but cannot be too large due to the size constraints of the measurement room Typical measurement distances found in technical literature are ranging from 4 to 8 meters Feistel and Ahnert showed in an interesting paper on the subject 3 that for mea surements of complex data there is a critical frequency where the phase error reaches T 4 This maximum frequency is defined by
30. speaker is possible and can significantly reduce the amount of data to be gathered but currently commercial simulation softwares are using regular sampled data There are some interesting application as the reconstruction of the loudspeaker polar pattern using spherical 9 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 In theory an higher sampling can better follow the spatial pattern of the source but it takes more time to measure using our single microphone approach and more storage space for the measurement files The 5 degrees resolution for a complete sphere seems to be a good trade off between those factors The following image show the 2664 points to be sampled for a 5 degrees full sphere polar measurement set n obo oo ug B gn gU Pah dart Oo B B LES Figure 6 Full sphere measurement points The following table reports the number of measurements the estimated completion time and the storage space a 5 degree resolution balloon measured with a MLS size of 16k with CLIO 10 and two Outline ET250 3D turntables in an anechoic chamber Number of Estimated Storage points time h mm space MB Full sphere 2664 2 45 670 Half sphere 1369 1 25 355 Quarter sphere 703 0 45 182 Polars only 144 0 09 38 Using a different resolution for the polar and the azim
31. ty model The GSS model is created using the EASE SpeakerLab software which is available with the electroa coustic modeling software EASE The EASE SpeakerLab can import set of time data impulse responses with CLIO format and naming scheme Using the export feature of the 3D CLIO menu it is possible to create a set of text files as requested by the EASE SpeakerLab In order to prepare the file needed by EASE SpeakerLab the Impulse Responses output format must be choose Selecting the Enable Truncation and Truncate Text Files limit the disk space usage by Saving smaller text file containing only the time data points into the valid measured time window The settings of the Balloon Export menu are reported in figure 24 Pressing the OK button on the Balloon Export menu will start the export process this again will take few minutes At the end of the export process we should have a folder with the impulse responses as txt files with naming convention IR phi 100 lt theta 100 gt txt The folder is ready to be imported with EASE SpeakerLab 14 Note that the export process every mls file in the origin folder if the source is sampled with finer resolution CLIO will show 5 degree data on its balloon visualization but export all the measurements i e with the finer resolution in txt time data format 27 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 WT up var Figure 23
32. ular sampling resolution must be a trade off between data set size measurement time and data accuracy For the simulation of the interaction between loudspeaker a regular sampling with 5 degree resolution seems a good tradeoff between data size and accuracy and is cur rently the standard in electroacoustic source polar measurement 7 As briefly outlined in the previous section the number of points to be measured can be reduced thanks to loudspeaker symmetry if available The symmetry that CLIO 10 can handle are None no symmetry the whole sphere needs to be measured Y NONE Half symmetry over the vertical plane HALF 11 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 Quarter symmetry over the horizontal and vertical plane QUARTER Axial axial symmetry a single polar is requested y AXIAL H V horizontal and vertical polar are interpolated mathematically y MEASUREMENT AUTOMATION WITH CLIO The CLIO 10 software can control the loudspeaker positioner two turntables and per form a complete automatic 3D polar measurement set The software take care of everything e execution of the measurements e management of the turntables to position the loudspeaker e saving of the measurements with a convenient naming scheme 9 This feature is intended to be used on magnitude only source models 12 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH
33. uth angle is possible this is the case of only horizontal and vertical polars with a given 9 resolution as low as 1 de gree as stated by some loudspeaker manufacturers and resolution 90 degrees The resolution to be used depends on the application of the polar data sets If the aim is the creation of simple horizontal and vertical polar patterns graphics there is no need to measure the full sphere balloon an horizontal and vertical polar measurement set is sufficient If the aim is the simulation of the complex interaction between acous harmonics where a non regular sampling can be adopted 7 In case of multiple microphone approach the hardware setup can also become very complex 8 This time is relative to the case of no delay between measurements that is in an anechoic environment In case of delay between measurements the delay times the number of measurements must be added to the estimated time As an example a full sphere balloon with a 2 second delay takes a total time of about 3 hours 10 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 tical sources a complete sphere balloon with complex data is needed When it s not possible to sample the source with the desired resolution interpolation of data is carried out The interpolation of polar sampled data is an interesting and quite complicated topic a treatment of this subject is outside the scope of this docu ment Here it is possible to state that the ang
34. uthor unregistered trial F Rogers 3d CLF yogers tab Figure 28 Directivity data imported in CLF reader viewer 32 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 CONCLUSIONS CLIO 10 feature a set of tools to automatically measure the 3D response of loud speakers analyze measured data sets and export data according to actual standards and simulation software needs The setup of a 3D measurement is simple and do not require any assistance reducing the manual intervention to the initial setup of the system The simple 3D visualization tool allow to check data consistency and to perform a first analysis of the results The CLIO 10 3D export feature allow to export data into the most common formats for source simulations REFERENCES 1 J D Appolito Testing Loudspeakers Audio Amateur Press 1998 2 CLIO 10 User s Manual Audiomatica 2009 www audiomatica com 3 S Feistel and W Ahnert The Significance of Phase Data for the Acoustic Prediction of Combinations of Sound Sources AES 119th Convention New York 2005 Octo ber 7 10 4 http en wikipedia org wiki Spherical coordinates retrieved 06 06 08 b C Struck S Temme Simulated Free Field Measurements JAES Vol 42 No 6 1994 June 6 S Feistel and W Ahnert Modeling of Loudspeaker Systems Using High Resolution Data JAES Vol 55 No 7 8 2007 July 7 AES56 2008 AES standard on acoustics Sound source modeling Lou
35. vity data The CLF models are created starting from a text file which contains the directivity tables along other source characteristics CLIO 10 is capable of automatically create a tab text file with the measured source directivity that comply with the CLF v2 specifications Here is it possible to use a measured on axis response or the on axis response of the balloon data it is also possible to shift the level of the on axis response to refer to the 1m 1w measurement distance and driving It is also possible to use a sin measurement of the source electrical impedance or as in this example use a nominal impedance value Here is a small strip of the file text created by CLIO 30 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 Balloon Export File amp Export Format Output format CLF v2 tab Dutput file F Rogers 3d CLF rogers tab General Information Loudspeaker Model Rogers Manufacturer 53 5 Frequency Hz ho 20000 On Axis Response Use Balloon Data Level Shift dB o o lt Calc Distance m 05 Drive Level w 025 Impedance Power Use Nominal Impedance ohm 19 Power w 100 Truncation m Ok Cancel Figure 27 CLF export feature lt CLE 2 gt VERSIONS 1 lt MODELNAME gt Rogers lt INFOFILE gt lt MANUFACTURER gt 5 3755 lt WEB SITE gt url SDESCRIFTION description lt COLORS gt MOUNTING
36. y a file set with a 5 degree resolution This is indeed a limitation together with the fixed third octave analysis frequencies but the 3D analysis module must be seen as a tool to briefly check the validity of the measured data set than an detailed inspection tool 18 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 Waterfall Directivity amp 3D Settings General Set OF Data Files Root File Hame Start Frequency Hz 22 m Stop Frequency Hz 122339 Symmetry Rotation Save Settings Default Cancel Figure 13 3D analysis settings 19 33 www audiomatica com AUTOMATED BALLOON MEASUREMENTS WITH CLIO 10 3 D 11 5 2009 3 24 22 PM 0 1 3 Octave Reference Balloon Range 24 dB Figure 14 Example of color balloon The allowed symmetries are exactly the same as in the case of automated measure ment none half quarter axial H V The Rotation parameter is the angle between the reference azimuth axis 0 of the measured data set and the reference azimuth axis of the balloon that will be created with the Root File Name data set This will be more clear later in the first example Pressing the go button the software checks if all the needed files are present then start the import process A progress window is showed since the task can take few minutes The required amount of time depends on many variables from MLS sizes of measurements to disk transfer rates At the en
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